Thanks for the article. It shows what I'd expect. I think Porsche choice for batteries in the 992 is inadequate to say the least. Can't start the car after 2-3 days from fully charged is bizarrely abnormal.

 

Canadian market cars are all lithium. In the US, rear axle steering cars get the lithium battery.

 

I'm confused, you said that after a few days your battery charge went down to 11-12 V. That's not bad at all.

 

Allegedly it is. From that to not starting is not a whole lot.
The problem is that the battery tops at 12.3 after days of charging, losing 0.4v overnight.

 

Some 992s have Li-Ion (LiFePo4) batteries and some have AGM. If you aren't sure, you need to LOOK. The really confusing thing is that some cars have a sticker that says Li-Ion even with an AGM battery - the sticker is NOT on the battery itself. Here's an early 992 (delivered in late 2019 according to the owner) equipped with an AGM (part# 992 915 105) battery that ALSO has a confusing Li-Ion sticker on the bracket above the battery:


I wonder if, due to that sticker, some folks are using battery maintainers in Li-Ion mode that actually have an AGM battery...

My 992 TTS battery is labeled LiFePo4 directly on the battery - and my bracket does NOT say Li-Ion - go figure:

 

Something is up with that. 12v should be enough.

On a battery maintainer, the battery charges fully to 15v, then is allowed to “discharge” down to 12 v before recharging again. At least that is what the battery maintainer instruction manual says. Something weird about what you’re experiencing

 

Now that my PSA (above) is out of the way...

A car that won't start 2 days after being on a trickle charger is just NOT right - sounds like a bad battery OR a bad trickle charger OR something wrong in the car itself (I hope not). I can't speak to the 992 w/AGM, but my two previous 991s with AGM would quickly drop to 12.3V after just a day without being charged - but the car would always start and I would sometimes let the car sit for a couple weeks without using the trickle charger at all. Maybe the 992 is more "vampiric" than the 991? I doubt it - my LiFePo4 equipped 992 doesn't even need a trickle charger - I've let it sit for 3 weeks without a problem so the 992 can't be drawing THAT much power.

It's interesting that on p55 of the owners manual (above) Porsche says you can go 6 weeks on a Lithium before you need to charge, but they don't provide any timeframe at all for AGM.

Two days and the car won't start is still just wrong, no matter what. Ask your dealer if you should reasonably expect to be able to park your car at the airport over a weekend.

 

I know and it's frustrating. They are the type of dealer that you show that the door handles don't pop out and they keep the car for a week and found nothing wrong. Unless it's a visible issue (and you run the risk of "wear and tear" excuse), they want a code on PIWIS. The concoction of issues suggests that one or more battery cells are bad. That's one of the reasons I wanted to know what other AGM cars are showing before starting and for how long people leave the car unattended without issues.

 

Testing the battery voltage at rest will tell you what its "health" is:

• Over 12.4 V: OK, good health;
• 12.0 - 12.4 V: will soon need a charge;
• Under 12.0 V: not OK; battery definitely needs a charge.

Now, if you charge the battery and, after letting it rest 60 to 90 minutes, it is under 12.4 V, this means you battery is not holding the charge......
..... and must be replaced!

https://batteryworld.varta-automotiv...ttery-test-car

 

See the following:

https://www.themechanicdoctor.com/ho...ry-sit-unused/

 

Doing some digging, interesting information from the AGM vendor. Note the graph in relation to temperatures. Things were really cold the past weeks in Chicago. Let's see what our RL friends from the Popsicle belt have to say. Still not good considering where these cars come from (unless our friends in cold Europe all get Lithium batteries)

https://www.bannerbatterien.com/download/?file=409

 

You can always replace the battery with a Lithium alternative. It's a consumable. I wouldn't get hung up on what yours came with.

 

Just back...car had sat in a semi exposed high rise garage in cold/snow for a little over a month and fired right up and drove beautifully all day! 50 and sunny in Chicagoland today!

 

I see a new battery on my future... looking into antigravity...

 

I have a Turbo scheduled to arrive in about 2 weeks. The garage I rent does not have power to connect a tender. I've never had a problem leaving my 991.2 GTS for 2 months without driving it. The garage does strangely enough have heat though.

I realize the Turbo has the Lithium battery which may be different but aren't even those supposed to last at least 6 weeks? Living in NY, especially this winter, makes it difficult to take the car out for extended drives and quite honestly I don't want to feel pressured to have to take the car out for drive just to keep the battery charged.

If I don't activate the Porsche connect services and the built in wifi would that help preserve the battery? Also is it better to leave the car unlocked? I'm trying to do whatever I can to help battery life.

Thanks